1. Field of the Invention (Technical Field)
The present invention relates to apparatus for measuring and imaging surface resistance in a superconductor; and a method of using the apparatus.
2. Background Art
The advent of numerous new, relatively high critical temperature, superconducting alloys and materials has brought with it a commensurate need to measure various properties of such materials, such as surface resistance and consistency. For example, U.S. Pat. No. 4,873,444, entitled Detection of Surface lmpurity Phases in High-Tc Superconductors Using Thermally Stimulated Luminescence, to Cooke, et al., discloses a process of detecting surface impurities by irradiating a sample with ionizing radiation, heating the irradiated sample to luminescence, and comparing the integrated luminescence with a calibration curve to determine surface resistance. This process, however, necessarily suffers from the disadvantage of testing the samples under normal conducting states, rather than under operational superconducting states.
"Morphology Control and High Critical Currents in Superconducting Thin Films in the Tl-Ca-Ba-Cu-O System," by D. S. Ginley, et al., Physica C, Vol. 160, pp. 42-48 (1989), discusses superconducting polycrystalline thin films in the Tl-Ca-Ba-Cu-O system with extremely high transition temperatures.
In "The Role of Low Temperatures in the Operation of Logic Circuitry," (Proceedings of the IEEE, Vol. 58, No. 12, pp. 1914-1932 (December 1970), R. W. Keyes, et al., discuss the suggested advantages and possible disadvantages of operative logic circuitry at low temperatures.
A. L. Schawlow, et al., in "Infrared and Optical Masers," Physical Review, Vol. 112, Number 6, pp. 1940-1949 (December 1958). discuss maser oscillation using resonant cavities of microwave dimensions.
K. E. Lonngren, et al., in an article entitled "On the Focused Fabry-Perot Resonator in Plasma Diagnostics," appearing in IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-12, pp. 548-549 (1964), discuss plasma diagnostics using a Fabry-Perot resonator at frequencies lower than microwave frequencies.
Wavemeter cavities for measuring surface resistance of superconductors are also known in the prior art, as disclosed in "Microwave Surface Resistance of YBa.sub.2 Cu.sub.3 O.sub.6.9 Superconducting Films," Appl. Phys. Lett., Vol. 52, No. 21, 23 May, 1988, pp. 1822-1824. While this process permits surface resistance measurement under superconducting conditions, the sample must be in contact with the cavity itself, complicating the measurement process and requiring additional energy to maintain cryogenic conditions.
Confocal resonators, that is, resonators, comprising two spherical mirrors with the center of curvature of each mirror at the other spherical surface, are also known in the prior art. Such resonators are known in the prior art, for example, for measuring dielectric constants of various insulating materials.